Time Dependent Adsorption of Ca^++ Ions onto a Langmuir Monolayer
Abstract
Recently, it was reported that the presence of Ca^++ ions in the water subphase increases the surface viscosity of arachidic acid monolayers at the air-water interface by three orders of magnitude over 15 hours [J. Chem. Phys. 111, 3675 (1999)]. The length of the time scales involved is puzzling in light of the extremely short time scales (< 10-7 s) associated with an individual Ca^++ ion adsorbing at an available site. Monte Carlo simulations based on a reversible random sequential adsorption model qualitatively explain how such a system could ``jam'' and ``unjam'', resulting in long time scales. As a test of the predictions of this model, we measured the amount of Ca^++ adsorbed onto a Langmuir monolayer film of arachidic acid as a function of time. This was done by transferring a known amount of monolayer onto a solid substrate by dipping the substrate into the film. The transferred film is dissolved in an acidic solution and the Ca^++ concentration is measured. We will present the results of these experiments and compare them with the model calculations.
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2000
- Bibcode:
- 2000APS..MARV31004G